The production of semiconductor devices, such as wafers, substrates, resulting integrated circuits, flat panel displays, data discs and other devices, often involves a variety of chemical processing steps. In some processes a liquid reactant is used which produces gaseous products. The production of gaseous products at the interface between the liquid processing fluid and the semiconductor piece can significantly effect the action of the reactant liquid upon the treated surface of the semiconductor material.
One example of chemistry which produces gaseous products involves the etching of silicon wafers (Si) using nitric acid (HNO.sub.3) and hydrogen fluoride (HF). The reactions between these acids and silicon produce nitrous oxides of various stoichiometric ratios, most typically considered nitrogen dioxide (NO.sub.2). The production of gases at the surface of the semiconductor piece causes the rate of reaction to be governed by diffusion through the gas-containing boundary layer. This diffusion limited rate characteristic of these and other reactions causes the processes to be more susceptible to rate variation across the wafer or other semiconductor piece. It also causes the reproducibility of the processes to vary to a greater degree than more typical liquid processes which are limited by chemical reaction rate mechanisms associated with the reactants rather than diffusion characteristics as in the reactions noted above.
Spray liquid and liquid immersion processes have previously been used to perform the gas-producing reactions explained above. These processes have suffered from the disadvantage that they expose both sides of a wafer to the chemical reaction and have variations in rate and reproducibility. Approaches to limit or protect exposure of the back side of the wafer have not been satisfactory because they do not fully protect the wafer or require significant additional processing time or additional processing materials.
Accordingly, there has remained a strong need for improved processing apparatus and improved processes for performing gas producing semiconductor processing.